Steam generator

ABSTRACT

The invention refers to a steam generator for household appliances. The steam generator comprises a container having an inlet for water and an outlet for steam, and an electrical heating element fixed to the container. The container comprises a first part and a second part which are connected along a joint such that a critical pressure inside the container causes a slit to appear in a predefined section of the joint, said slit providing a security vent for releasing pressure.

The invention refers to a steam generator for household appliances likewashing machines, laundry driers, electric irons, espresso machines orovens.

Such steam generators have an inlet for water and an outlet for steam.If the outlet is clogged a continued steam generation might cause adangerous increase of pressure and ultimately an explosion.

A steam generator suitable for household appliances is disclosed in DE10 2006 020 280 A1. The known device generates steam inside a containerconsisting of a bottom part and a lid part which are clamped together bya threaded bolt extending through the container. The bolt head pressesagainst the outside of the bottom part; a nut screwed onto the boltpresses against the outside of the lid part. A joint between the bottompart and the lid part is sealed by an elastic adhesive. If the pressureinside the container increases beyond a certain level the adhesive willfail and pressure vented through a rupture along the joint.

It is an object of the present invention to provide a steam generatorfor use in household appliances which is inexpensive to manufacture andprevents a dangerous increase of pressure by automatically venting ofsteam.

SUMMARY OF THE INVENTION

A steam generator according to the present invention comprises acontainer in which water is evaporated by means of an electrical heatingelement fixed to the container. The container has an inlet for water andan outlet for steam. The container comprises a first container part witha flange against which a second container part rests thereby coveringthe first part.

These two container parts are connected in such a way that a criticalpressure inside the container forces them slightly apart such that aslit appears between the two container parts at a predefined location.This slit provides a security vent for releasing pressure. In the casethat the steam outlet is clogged for any reason, even continued steamcreation cannot lead to an increase of pressure beyond the criticallevel that causes the security vent to open. Therefore, the containercannot explode.

An important advantage of the present invention is that the slit orslits will open at a predefined location. Whereas prior art steamgenerators, like those known from DE 10 2006 020 280 A1, vent steam in arandom direction where the steam may cause damage, such damages can beprevented according to the invention by choosing the predefined locationaccordingly.

In an embodiment of the invention the first and the second containerpart are fixed to each other along part of their circumference, forexample by clamping, which may be achieved by at least one rim sectionof one of the container parts that is folded over a rim section of theother container part. In this way the two container parts aremechanically connected. However, according to the invention the twocontainer parts are firmly connected only along part of theircircumference. For example, along a first part of the circumference therim of one of the container parts may be covered by a folded rim sectionprovided at the other container part and along a second part of thecircumference the rim of both container parts is not covered by suchfolded sections. Another possibility is to arrange a welded seam or aseries of weld spots or rivets along a first part of the circumference,but not along a second part.

In the second part of the circumference the two container parts aretherefore not fixed to each other and can be forced apart much moreeasily than in the first part. Should the pressure inside the containerrise to an overly high level the container will therefore open slightlyalong the second part of the circumference enabling steam to escape.Advantageously, such venting may be achieved without destruction of thedevice.

In a preferred embodiment of the invention the security vent, whichopens between the two parts of the container when the pressure in thecontainer exceeds a critical threshold value, is used as a second safetyfeature in combination with a conventional overload valve at the steamgenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will be betterunderstood by the following description when considered in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a side view of an embodiment of the present invention;

FIG. 2 a bottom view of the container of the steam generator shown inFIG. 1;

FIG. 3 is a cross section along line AA of FIG. 2; and

FIG. 4 is a cross section along line BB of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows a steam generator 1 comprising a disc-shaped container 2and an electrical heating element 3 fixed to the outside of thecontainer 2. The container 2 has an inlet 4 for water an outlet 5 forsteam.

The container 2 comprises a bottom part 2 a having a flange 6 and a lidpart 2 b resting against the flange 6 thereby covering the bottom part 2a. In the example shown these two container parts 2 a, 2 b are ofsubstantially equal shape and the lid part 2 b is also provided with aflange 7. Although in principle the lid part 2 b might simply be a flatdisc.

The two container parts 2 a, 2 b are fixed to each other by clamping.The clamping forces are caused by rim sections 8 of one of the containerparts 2 a, 2 b which are folded over the rim of the other containerpart. In the example shown, rim sections 8 of the lid part 2 b arefolded over the rim of the bottom part 2 a. Such rim sections 8 mightjust as well be provided on the bottom part 2 a and folded over the rimof the lid part 2 b. It is also possible to provide one or severalfolded rim sections 8 on both the bottom part 2 a and the lid part 2 b.

The folded rim sections 8 cover only part of the circumference of thecontainer 2. Therefore the clamping forces act only on a part of theflanges 6, 7, i. e. on first sections but not on second sectionsadjacent to the first sections in a circumferential direction. This canbe seen especially well in FIG. 2 which shows a bottom view of thecircular container 2 without the heating element. There is a series ofsections of the flanges 6, 7 where folded rim sections 8 are provided,by which the flanges 6 and 7 are clamped together. Sections 9 and 11 inbetween the folded rim sections 8 are not clamped together.

Partly the circumference of the device 1 is covered by folded rimsections 8 and therefore is clamped as illustrated in FIG. 3 showing across section along line A-A of FIG. 2. Along at least one second partof the circumference there are no folded rim sections, i.e. neither therim of the bottom part 2 a nor the rim of the lid part 2 a is covered bya folded rim section as illustrated in FIG. 4 showing a cross sectionalong line B-B of FIG. 2. No clamping forces act on this at least onesecond part of the circumference.

In the example shown, this at least one second part of the circumferencecomprises two larger venting sections 9 between folded sections 8. Theseventing sections 9 are indicated in FIG. 2 by dotted lines enclosing anangle α.

The venting sections 9 provide a security feature preventing a dangerousbuild up of pressure in the container 2. If the steam outlet 5 isobstructed for any reason, continued steam generation causes pressure inthe container 2 to increase. Unchecked, such an increase mighteventually cause the container 2 to explode. This is prevented by theventing sections 9. As the bottom part 2 a and the lid part 2 b are notfixed to each other along the venting sections 9, an increase inpressure beyond a certain level will force the bottom part 2 a and lid 2b slightly apart elastically in this venting section 9 of thecircumference. Thus a critical pressure inside the container 2 causes aslit to appear in a predefined venting section of the joint along whichthe two container parts 2 a, 2 b are connected. This slit provides asecurity vent for releasing pressure which will always open elasticallywhen needed and will close when the pressure dropped to an uncriticalvalue.

In order to open reliably without damaging the container 2, the ventingsections 9 preferably should have a length of at least one eighth of thetotal length of the circumference. In the example shown, each ventingsection 9 has a length of about one seventh of the total length of thecircumference. The smaller sections 11 between the folded sections 8 ofthe illustrated container 2 are too small to enable venting and are notnecessary. In principle a single large folded section 8 covering asufficiently large part of the rim would be sufficient. However, it iseasier to fold several smaller sections 8 instead of one larger section.

In principle, one sufficiently large venting section 9 is sufficient toprevent a dangerous increase of pressure. In general, the ventingsection 9 should have a length of at least one tenth of thecircumference and at most one third of the circumference. Larger ventingsections 9 could cause the container to open too easily. Preferably, theventing sections 9 have a length of not more than one quarter of thetotal length of the circumference. Preferably, the venting sections 9should have a length of one eighth to one quarter of the circumference.

The bottom part 2 a and the lid part 2 b are made of sheet metal, forexample by deep drawing of a sheet of stainless steel. Therefore, thecontainer 2 should have rather thin walls of less than, 0.7 mm,preferably less than 0.6 mm, most preferably 0.4 to 0.5 mm. As aconsequence, the container 2 has a favourably low heat capacity and canbe heated up quickly for steam generation. The volume of the container 2is about 50 ml to 400 ml, preferably 150 ml to 300 ml. To obtain such avolume the overall diameter of the container 2 may be 10 cm to 20 cm andpreferably is selected to be 13 to 15 cm.

To seal the container 2 during normal operation, a seal 10 is compressedbetween the flange 6 of the bottom part 2 a and the lid part 2 b. Theseal 10 may be a gasket, for example an O-ring as shown in FIGS. 3 and4. Alternatively, the seal 10 may be a strand of adhesive. In theembodiment shown, the seal 10 is arranged in a groove of the flange 6 ofthe bottom part 2 a. The flange 7 of the lid part 2 b may also have agroove which encloses an upper part of the gasket seal.

1. Steam generator comprising a sheet metal container having an inletfor water and an outlet for steam, and an electrical heating elementfixed to the container, the container comprising a first container partand a second container part which are clamped together, the first parthaving a flange against which the second part is clamped covering thefirst part, and a seal arranged on the flange, said seal beingcompressed between the first container part and the second containerpart, wherein the first container part and the second container part areclamped together by clamping forces acting on at least one first sectionof the flange but not on at least one second section of the flangeadjacent in circumferential direction to the at least one first section,the clamping forces being applied such that a critical pressure insidethe container causes a slit to appear between the at least one secondsection of the flange and the second container part, said slit providinga security vent for releasing pressure.
 2. Steam generator according toclaim 1, wherein the clamping is effected by sections of the firstcontainer part folded over a rim of the second container part.
 3. Steamgenerator according to claim 1, wherein the clamping is effected bysections of the second container part folded over a rim of the flange ofthe first container part.
 4. Steam generator according to claim 1,wherein the seal is a gasket.
 5. Steam generator according to claim 4,wherein the gasket is arranged in a groove of the flange.
 6. Steamgenerator according to claim 1, wherein the second container partcomprises a flange which rests against the flange of the first containerpart.
 7. Steam generator according to claim 1, wherein the container isa circular disc.
 8. Steam generator according to claim 7, wherein the atleast one second section has a length of one eighth to one quarter ofthe circumference of said circular disc.
 9. Steam generator according toclaim 7, wherein the at least one second section has a length of oneseventh to one fifth of the circumference of said circular disc. 10.Steam generator according to claim 1, wherein at least one of thecontainer parts is made of a sheet metal.
 11. Steam generator accordingto claim 7, wherein the container has an overall diameter of 10 cm to 20cm.
 12. Steam generator according to claim 7, wherein the container hasan overall diameter 13 cm to 15 cm.
 13. Steam generator according toclaim 1, wherein the heating element is fixed to the outside of thecontainer.
 14. Steam generator according to claim 17 wherein the atleast one second section of the flange has a length of at least onetwelfth of the circumference the flange.
 15. Steam generator accordingto claim 1, wherein the at least one second section of the flange has alength of at most one quarter of the circumference the flange.
 16. Steamgenerator according to claim 1, wherein the first container part and thesecond container part are of equal shape.
 17. Steam generator comprisinga container having an inlet for water and an outlet for steam, and anelectrical heating element fixed to the container, the containercomprising a bottom part as a first container part and a lid part as asecond container part which rests against a flange of the bottom part,wherein these two container parts are fixed to each other along part oftheir circumference by at least one rim section of one of the twocontainer parts that is folded over a rim section of the other containerpart, such that along a first part of their circumference the rim of oneof the container parts is covered by the other container part and alonga second part of their circumference the rim of both container parts isuncovered, wherein the second part of their circumference comprises aventing section having a length of at least one tenth of thecircumference and at most one third of the circumference, said sectionproviding a vent which opens in the case of the pressure exceeding acritical threshold.
 18. Steam generator according to claim 17 whereinthe venting section has a length of one eighth to one quarter of saidcircumference.
 19. Steam generator according to claim 17, wherein theventing section has a length of one seventh to one fifth of saidcircumference.
 20. Steam generator according to claim 17, wherein thecontainer part comprising the folded rim section or sections is made ofa sheet metal.
 21. Steam generator according to claim 17, wherein boththe lid part and the bottom part are made of a sheet metal.
 22. Steamgenerator according to claim 17, wherein the container has an overalldiameter of 10 cm to 20 cm.
 23. Steam generator according to claim 17,wherein the container has an overall diameter of 13 cm to 15 cm. 24.Steam generator according to claim 17, wherein the container has a wallthickness of less than 0.7 millimeters.
 25. Steam generator according toclaim 17, wherein the container has an wall thickness of 0.4 mm to 0.5mm.
 26. Steam generator according to claim 17, wherein the container hasa volume of 50 to 400 milliliters.
 27. Steam generator according toclaim 17, wherein the container includes a volume of 150 to 300 ml. 28.Steam generator according to claim 17, wherein the bottom part and thelid part are of equal shape.
 29. Steam generator according to claim 17,wherein a gasket is placed between the flange of the bottom part and thelid part.
 30. Steam generator comprising a container having an inlet forwater and an outlet for steam, and an electrical heating element fixedto the container, the container comprising a first container part and asecond container part which are connected along a joint, the firstcontainer part having a flange against which the second container partrests covering the first container part, and a seal compressed betweenthe first container part and the second container part, wherein thefirst container part and the second container part are connected suchthat a critical pressure inside the container causes a slit to appear ina predefined section of the joint, said slit providing a security ventfor releasing pressure.
 31. Steam generator according to claim 30,wherein said slit in the joint occurring between the first containerpart and the second container part responsive to a critical pressureinside the container opens as a result of an elastic deformation of atleast one of said first container part and said second container partand will close again by the container parts reducing their elasticdeformation as the pressure in the container decreases to an uncriticalvalue.